Getting Started

To get started, all you really need is a git clone. After that, you can compile and run the latest-and-greatest (and maybe buggy) versions of the KDE PIM applications.
When you find a bug, you can fix it, create a patch, and send it to us! That's the way KDE PIM applications are continually improving. There is much more information available to begin with, though.

Here is a checklist of things to launch yourself into the world of KDE PIM development.
For lots of them, it is most important that you know they exist:

Get the prerequisites for building KDE PIM master. Note that you really want to follow master to make a positive contribution to KDE PIM.

If you work on or with the last released version, you're usually a month or four behind the times, and that makes a huge difference in KDE PIM. You can work with a stable system -- the latest released KDE libs and base -- and put (relatively) unstable PIM HEAD on it.

Mailing Lists

Mailing lists are probably the ultimate source of development information. Follow discussions of KDE core and application developers and ask your questions. Unless you don't think about what you are saying, you will surely get an answer. Subscribe to the kde-pim mailing list. It is for discussion about development. Please don't wildly post all your compilation problems there. Ask on IRC for such issues.

IRC (Chat)

Most of the developers hang around in one development IRC channel or another. On freenode (irc.kde.org), you can find:

#KDE for the user questions.

#akonadi for development discussion on Akonadi.

#kontact for development discussion on Kontact and its components. Please don't post user-questions there.

There are a variety of IRC (Chat) programs available. KDE ships with Konversation. XChat is available in many installations as well.

KDEPIM-RUNTIME, the Akonadi resources which are required at runtime to let the kdepim applications communicate with the Akonadi server

KDEPIM, All the PIM applications

In order to build and use the KDEPIM modules, you may use the last released KDE version.

You might want to make a backup of your valuable data, though. Most of it lives in .kde, in your home directory; You may also backup your Akonadi server config files in $HOME/.config/akonadi and your kdepim applications data in $HOME/.local/share.
It may be easier to just create an additional user and give it a copy of your data, and run PIM HEAD there.

The little longer guide

If you are in the position to have a distribution (debian,ubuntu,...) , that doesn't ship the newest kde stable version you have to build more packages.
First you should get the two really fancy scripts build-config, findup, kde-bashrc from Getting Started/Build/Environment. For the next part I assume that you have following layout and would suggest to create a dececated user: